The translation of bones or implants attached thereto during surgery, whether it be to humans or other animals, often requires the surgeon to carefully apply relatively significant forces. A common solution to accurately controlling the effects of the forces is to apply the forces in pulse increments, with the pulse characteristics defining a pulse force with limited translation. This form of applied force limits the obvious risk of producing an undesired excess in the translation of a bone or implant.
The particular context within which the present invention is preferably practiced involves the removal of orthopedic implants. In that context, the surgeon is attempting to forcefully extract implants from bone structure while in a sterile hospital environment with minimum size and power equipment. An existing device for accomplishing this function is often referred to as a "slap hammer", the title due largely to the nature of its operation. The structure and operation are analogous to those utilized by automobile mechanics and body repairmen in moving parts using a sliding hammer tool.
In the context of orthopedic implant extraction, the device consists of a guide rod and a sliding weight. A clamp is affixed to the surgically exposed implant and the device is threaded into the clamp. The sliding weight on the device is thrown upward, generating a jerking force when the momentum of the moving weight is converted to a pulse of force upon striking stop on the end of the guide rod. With repeated throws of the sliding weight the pulses of force extract the implant.
Though the "slap hammer" orthopedic implant extraction device is functional in accomplishing basic removals of implants and the like, it is heavy (5-10 pounds), is awkward to handle (requires two handed operation), and is not readily amenable to changes in force characteristics (intensity and duration) as may be sought during an extraction sequence. Though pneumatically operated hammers are known for automotive applications, their size and control characteristics do not lend themselves to orthopedic implant extraction or the like medical procedures.
Similar controllability concerns exits in the orthodontic practices, where extractions of teeth often occur only when the dentist or oral surgeon is pulling at his or her physical limits.
What is needed is a pneumatically operated medical actuator that has structural features which allow it to be light in weight yet fully capable of significant force pulses, that has actuation characteristics which lend themselves to single hand operation, and that provides control resources suitable to create selective pulses encompassing pulse width as well as pulse frequency modulation. Attainment of the foregoing beneficial features should not be done at the sacrifice of structural simplicity, an important consideration for the cleaning and sterilization associated with medical procedures. Likewise as to the importance of design features which allow use with the gases at the pressures available in conventional medical and dental operating rooms.